Method For Stabilizing The Spine

ABSTRACT

Spine stabilization systems and integrated rods are disclosed. One spine stabilization system disclosed has at least four bone anchors and a stabilization member attached to the bone anchors. The stabilization member has first and second elongate portions interconnected by a connector portion. The first and second elongate members extend longitudinally and generally parallel to a central longitudinal axis and connector portion extends transverse to the central longitudinal axis from a first lateral end to a second lateral end. The connector portion is integrally connected to the first and second elongate portions such that there is no relative movement between the lateral ends and the respective elongate portion to which each end is attached.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation application claiming priorityto U.S. patent application Ser. No. 12/014,025 filed on Jan. 14, 2008,the entire contents of which are incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to a spine stabilization system.In particular, certain embodiments are directed to an integratedstabilization member having increased torsional strength.

BACKGROUND OF THE INVENTION

The human spine is particularly important because it protects the spinalcord, which is responsible for relaying electrical impulses from thebrain to the rest of the body. Occasionally, an accident or otheroutside force may cause the vertebrae which make up the spine to bebroken, cracked, or chipped. Each of these situations are dangerous, andare handled by the most skilled physicians and surgeons. The remedy fora broken, cracked, or chipped bone may be different for everyindividual, and may change according to the situation under which theinjury occurred.

One situation that commonly arises occurs is when vertebrae or portionsof vertebrae or spine are broken, cracked, or are beginning to fail tofunction normally. One treatment technique used by doctors to remedythis situation involves using a pair of rods that are connected toseveral vertebrae. The rods may be aligned along the periphery of thevertebrae, and are typically used to maintain the alignment of thebones. This may allow the vertebrae to re-grow bony tissue or cartilage.In addition, aligning the vertebrae allows them to heal properly, andprevents movement of the spine from injuring the spinal cord.

In order to prevent the movement of the spine, a fixation system isoften used to hold the two rods together. The fixation system allows therods to be fixed in place under normal conditions. Many fixation devicesare currently available. They vary in shape, size, and their approach topreventing the rods from moving. One type of device that has been usedinvolves a single connection body that lies in between the two rods,over the body of the vertebrae. Though this device serves the purpose ofpreventing the rods from moving, it also has several disadvantages. Forexample, many of these devices are unable to move, rendering them unableto adapt to the contour of the spine. Another limitation of thesedevices is that they typically do not allow for clearance of the body ofthe vertebrae, which can cause damage to the vertebrae or cause thedevice to protrude from underneath a person's skin.

Many devices hold the rods in place by gripping them from the outerportion of the bars. These devices also achieve the purpose of holdingthe bars in place, but have several limitations. For instance, thesedevices often may not be capable of achieving the same degree of grip onthe rods as compared to a configuration that grips the bars from theinner area, between the bars.

Other devices have aimed to eliminate the limitations of theirpredecessors by providing two connecting bodies that have a small degreeof adjustability. However, many of these devices are unable to translateaxially, which prevents them from adjusting to the spacing between therods. Other devices are unable to rotate to adjust for rods that aren'tcoplanar. Additionally, these devices often do not have the ability torotate freely, preventing them from adjusting to the contours of thespine. Devices such as these may provide greater adjustability at theexpense of increased complexity, number of components, increased overallheight, or other limitations and disadvantages.

A continuing need exists for a spinal fixation system that is able toadjust the contours of the spine, is simple to install and meets thedemanding mechanical loads that are experienced when implanted in apatient.

BRIEF DESCRIPTION OF THE DRAWINGS

Spine stabilization systems and integrated rods are disclosed. One spinestabilization system has at least four bone anchors and a stabilizationmember attached to the bone anchors. The stabilization member has firstand second elongate portions interconnected by a connector portion. Thefirst and second elongate members extend longitudinally and generallyparallel to a central longitudinal axis and connector portion extendstransverse to the central longitudinal axis from a first lateral end toa second lateral end. The connector portion is integrally connected tothe first and second elongate portions such that there is no relativemovement between the lateral ends and the respective elongate portion towhich each end is attached.

In one variation, the width of the connector portion adjacent to theelongate portions is less than 5 mm when viewed from the side. Inanother variation, the connecting portion is fixably telescopinglyextendable in the lateral direction transverse to the centrallongitudinal axis to selectably vary the lateral separation of theelongate portions and all other degrees of freedom are fixed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of a stabilization systemaccording to the invention;

FIG. 2 is a perspective view of one embodiment of a stabilization memberof the system of FIG. 1;

FIG. 2 is a perspective view of one embodiment of a stabilization memberof the system of FIG. 1;

FIG. 3 is a perspective view of the stabilization member of FIG. 2 shownin a laterally expanded condition;

FIG. 4 is a side view of the stabilization member of FIG. 2;

FIGS. 5-7 are perspective, front, and side views of one embodiment of anarm of a connector portion of the stabilization member of FIG. 2;

FIGS. 8-10 are perspective, partial cross-section front, and side viewsof another embodiment of an arm of a connector portion of thestabilization member of FIG. 2;

FIG. 11 is a perspective view of one embodiment of an elongate member ofthe stabilization member of FIG. 2;

FIG. 12 depicts one step in an embodiment of a method of installation ofa stabilization system according to the invention; and

FIG. 13 depicts another step in an embodiment of a method ofinstallation of a stabilization system according to the invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Embodiments of the present invention are generally directed to a spinestabilization system. In particular, certain embodiments are directed toan integrated stabilization member having increased torsional strength.

Referring now to FIG. 1, one embodiment of a stabilization system 5according to the invention is shown. Stabilization system 5 generallycomprises four bone anchors 8 attached to bone and a stabilizationmember 10 rigidly attached to the bone anchors. As best seen in FIG. 2,stabilization member 10 generally comprises first and second elongatemembers or rods 12, 14 interconnected by connector portion 16. In onevariation, first and second elongate members extend longitudinally andgenerally parallel to a central longitudinal axis 18 and connectorportion 16 extends transverse and generally perpendicular to axis 18. Inthis regard, when stabilization member 10 is viewed from the top, suchas when viewed as implanted in a patient as shown in FIG. 1, it has ageneral H-like shape.

The opposing ends 20, 22 of connector portion 16 are generally rigidlyor fixedly connected to elongate members 12, 14 such that there is norelative movement between the ends 20, 22 and the respective elongatemembers 12, 14 to which each end is attached. In one variation,elongated members 12, 14 and connector portion 16 may be a unitaryconstruction manufactured from the same block of material. In anotherembodiment, connector portion 16 may be manufactured to be immovablyconnected to elongate members 12, 14 by welding. In one variation, alaser weld may be used to fix connector portion 16 to elongate members12, 14. In this regard, as shown in FIG. 2, ends 20, 22 of connectorportion 16 may extend around the entire periphery of elongate members12, 14 and a 360° weld may be applied to attach connector portion 16 toelongate members 12, 14.

Referring to FIGS. 2-3, in one embodiment connector portion may providefor telescoping movement in the lateral direction transverse to axis 18.In this regard, elongate members 12, 14 may be variably spaced laterallyapart to accommodate patient anatomy. In one embodiment, the laterallength 23 of connector portion 16 may be selectively varied betweenabout 30 mm and 90 mm, and in another embodiment the lateral length maybe adjustable between about 38 mm and 71 mm. In this regard, accordingto this variation, the only relative movement between the elongateelements is lateral movement with all other degrees of freedom fixed.One skilled in the art may appreciate the simplicity involved with suchlimited adjustability as less fidgeting is required to install thestabilization member. Also, such a streamlined design may decreaseoperating time by reducing insertion steps since a surgeon does not needto separately attach a transconnector device in situ.

In one embodiment of a laterally telescoping stabilization member 10,connector portion 16 comprises an extender arm portion 24 telescopinglyreceived within a receiver arm portion 26. Referring to FIGS. 5-6,extender arm portion 24 of connector 16 generally comprises an elongateshaft portion 28 extending medially opposite lateral end 20. Shaftportion 28 is configured and dimensioned to be received within channel30 which extends medially within receiver arm portion 26. In onevariation, a generally flattened upper surface 32 extends along at leastpart of shaft portion 28 to facilitate a set screw 33 to fixedly clampthe shaft portion of extender arm 24 within the channel 30 of receiverarm 26. As seen in FIGS. 8-10, a hole 35 may be provided to accommodatethe set screw such that the extent of lateral offset may be fixedlyadjusted. In alternative embodiments, alternative adjustable telescopingmeans known to those skilled in the art may be provided to facilitatelateral adjustability of the elongate members 10, 12.

Referring to FIGS. 5-6 and 8-9, according to one embodiment, the lateralends 20, 22 respectively of connector portion 16 comprise an eyelet orthrough hole 36 to receive an elongate member therethrough. In onevariation, hole 36 may be generally cylindrical and may have a diameterslightly larger than the elongate member to which it is to attach. Inthis regard, referring to FIG. 11, elongate members 12, 14 may have aradially raised section 39 with additional material or larger diameterregion configured and dimensioned to interface with the interior regionof hole 36. Such additional material may facilitate the weldingattachment of the respective connector portion to the respectiveelongate member. For example, since the junction between the connectorportion and the additional material is slightly spaced from theperimeter of the elongated element, the rod is less of a direct heatsink during the welding process which ends up requiring less energyduring the weld and provides for efficient manufacturing. The additionalmaterial provided adjacent the weld junction may also allow for thecreation of a fillet around the entire periphery of the elongate memberthereby creating a strong mechanical joint resistant to high torsionalloads.

Referring to FIG. 10, in another aspect of the invention, the width 40profile of the connector portion 16 adjacent to the elongate elements12, 14 when viewed from the side is smaller than width profile 42 of theconnector portion 16 spanning between the elongate members. In thisregard, the narrowing of the connector portion 16 provides a smaller runon the rod, as best seen in FIG. 4, than would be possible without suchnarrowing. In other words, less space is taken up along the length ofthe elongate members 10, 12 to accommodate the attachment of connectorportion 16 thereto. For example, as best seen in FIG. 4, according toone embodiment the width 40 along the rod is less than 5 mm and in otherembodiments the width is less than 4 mm. Those skilled in the art willappreciate that with such a smaller run on the rod, the spacing ofadjacent anchor members may be commensurately shortened. Such a featuremay be advantageous, for example, in procedures where the anchors aretypically inserted with such a small separation distance, such as thefixation of the L5-S1 segment.

In one embodiment, best shown in FIG. 7, the cross-section of thecentral portion of connector 16 is generally ovoid having a height 44that is between about 6 mm and 9 mm and a width 46 that is between about5 mm and 8 mm. In one embodiment, height 44 is about 7.5 mm and width 46is about 6.5 mm. However, the precise geometry is not critical and inalternative exemplary embodiments, the central portion of connector 16may have a hexagonal, cylindrical, square, or any other geometriccross-section as those skilled in the art may contemplate. In anotheraspect of the invention, best shown in FIG. 9, the lateral ends 20, 22of connector portion 16 may be angled upwards from the rod toaccommodate the natural anatomy such that the connector portion mayextend over posterior elements of the spine. In one embodiment, theangle 48 may be between about 20 and 60 degrees and in anotherembodiment angle 48 may be about 40 degrees.

According to some embodiments, as shown in FIG. 1, elongate members 12,14 may have a generally circular cross-section. In one variation,elongate members 12, 14 may comprise a rod having a circularcross-section between about 5 mm and 7 mm, and in particular betweenabout 5.5 mm and 6.35 mm. However, the precise geometry is not criticaland in alternative exemplary embodiments, elongate members 12, 14 mayhave a hexagonal, elliptical, square, or any other geometriccross-section as those skilled in the art may contemplate. Also,elongate members 12, 14 need not have the same cross-section, nor is itnecessary that the cross-sections be uniform along the length. Elongatemembers 12, 14 may be provided in a wide variety of lengths andprofiles. For example according to one variation, elongate members 12,14may be provided in lengths ranging from about 30 mm to about 120 mm andin other embodiments lengths between about 40 mm and 100 mm may beprovided. Similarly, elongate members may be bent or contoured to, forexample, generally approximate the natural anatomy of the spine regionwhere it is to be implanted, among other things. In this regard,elongate elements 12, 14 may be pre-contoured or bent by a physician insitu. For example, as shown in FIGS. 1 and 2, stabilization member 10 isshown with a generally curved profile with connector portion 16extending across the concave side of elongate members 12, 14. Again thelengths and profiles need not be the same for each elongate member 12,14.

Referring now to FIGS. 12-13, one embodiment of a method of installationis shown. According to one variation, anchors or bone screws areinserted into pedicles of the thoracolumbar and/or sacral spine. In onemethod, four bone screws 8 are inserted into the four adjacent pediclesto one spinal segment, such as for example between the L5 and S1 spinalsegment. Attachment of the stabilization member 10 to the pedicle screwsis dependent on the pedicle screws used in the construct. The size andnumber of screws are dependent on the length and location of thestabilization member 10.

In another variation, the appropriate rod contour and length of thestabilization member 10 may be determined using a rod template. Ifnecessary, one or both of the elongate members or rods 12, 14 may bebent or contoured using a rod bender. A rod cutter may also be used tocut the implant to the appropriate length.

As shown in FIG. 12, the integrated stabilization member 10 may be toploaded into the screw heads using a rod holder 50. Once loaded into thescrew heads, the stabilization member 10 may be secured to the pediclescrews 8. In one method, a locking cap driver may be used to install alocking cap 52. The driver may be rotated to engage the locking cap 52into the screw head and capture the elongate members 12, 14 ofstabilization member 10. A set screw within the locking cap may betightened to secure the construct. As shown in FIG. 13, the lateraloffset of rods 12, 14 may be secured by tightening the set screw 33using a driver 54.

Stabilization members 10 according to the invention may comprise anymaterial, or combination of materials suitable for implantation in thehuman body. The materials may include, but are not limited to, a metalor alloy. In some embodiments, steel, titanium, iron, and the like maybe used. The type of material that is used may be chosen such that ithas sufficient strength to maintain the elongate members 12, 14 in asubstantially fixed manner under normal conditions. Normal conditions,as described, will be understood to be conditions that a healthy spinemay be subjected to without causing the structural integrity of thevertebrae to be compromised. For example, it is estimated that thetorsional stiffness of the human thoracolumbar spine is about 1.2 N-mper degree of axial rotation and cyclical torsional loads producing morethan +/−1.5° of angular displacement per spinal segment are detrimentalto elements of the lumbar spine. As a result, it is estimated that themaximum torque that will be effectively resisted by the thoracolumbarspine is about 1.8 N-m. Thus, using a material that is capable ofmaintaining its structural integrity when subjected to the conditionspresent inside the human body is desired. In one embodiment,stabilization member 10 is made from a titanium alloy and the torsionalstiffness is at least 4 N-m/degree. Those skilled in the art mayappreciate that such a relatively increased torsional stiffness mayreduce torsional load on screws, minimizing the risk of constructbreak-down.

Example

In a static torsional test method used conforming to ASTM standardF1717, five constructs similar to that shown in FIG. 1 (i.e. with astabilization member 10 attached to four anchors) were tested. Torqueand angular displacement were recorded. Static torsional tests wereperformed in displacement control at a rate of 30°/min, starting at zerotorque and ending at failure of a maximum angular displacement of 60°.Yield load was calculated using the 2% offset yield criterion, per theASTM standard F1717. All five specimens were tested in static torsionand exhibited an average torsional stiffness of 5.7 N-m/Degree. Asimilar construct without a transconnector was also tested using thesame methods and exhibited an average torsional stiffness of 1.9N-m/Degree and another construct having a non-integrated conventionaltransconnector exhibited a torsional stiffness of 3.4 N-m/Degree usingthe same test.

While it is apparent that the invention disclosed herein is wellcalculated to fulfill the objects stated above, it will be appreciatedthat numerous modifications and embodiments may be devised by thoseskilled in the art.

1. A method for stabilizing the spine, comprising the steps of:positioning a first set of least two bone anchors on a first side of thespine; positioning a second set of least two bone anchors on a secondside of the spine; positioning a first elongated rod of a stabilizationmember into the first set of at least two bone anchors; pivoting thefirst elongated rod to position a second elongated rod of thestabilization member into the second set of at least two bone anchors;locking the first elongated rod within the first set of at least twobone anchors; locking the second elongated rod within the second set ofat least two bone anchors; wherein the stabilization member the firstand second elongate rods are interconnected by a connector portion, theconnector portion extending transverse to a central longitudinal axisfrom a first lateral end to a second lateral end; wherein the connectorportion is integrally connected to the first and second elongateportions such that there is no relative movement between the lateralends and the respective elongate portion to which each end is attached.2. The method of claim 1, wherein the connector portion is immovablyconnected to elongate portions by welding.
 3. The method of claim 2,wherein a laser weld may be used.
 4. The method of claim 2, wherein thelateral ends of connector portion extend around the periphery ofelongate portion and a circumferential weld may be applied to attachconnector portion to elongate portions.
 5. The method of claim 1,wherein the width of the connector portion adjacent to the elongateportions is less than 4 mm when viewed from the side.
 6. The method ofclaim 1, further comprising the step of telescopingly positioning thestabilization member in the lateral direction transverse to the centrallongitudinal axis to vary a lateral length of the connector portion. 7.The method of claim 6, further comprising the step of selectivelyvarying the lateral length of the connector portion between about 30 mmand 90 mm.
 8. The method of claim 6, further comprising the step offixing the only relative movement between the elongate portions islateral movement and all other degrees of freedom.
 9. The method ofclaim 2, wherein the torsional stiffness is at least 4 N-m/Degree whenmeasured in a static torsional test conforming to ASTM standard F1717.10. The method of claim 2, wherein the torsional stiffness is at least5.7 N-m/Degree when measured in a static torsional test conforming toASTM standard F1717.